Fuel in an aircraft is typically stored in one or more fuel tanks. Such fuel tanks are generally disposed in the interior space of the wings and fuselage of the aircraft. A fuel delivery arrangement including a fuel pump is arranged to draw fuel from the or one of the fuel tanks and provide the fuel to one or more engines.
In one arrangement, a fuel pump is disposed in the fuel tank which draws fuel from the tank and feeds it along a pipe to be used by the one or more engines.
Due to the necessary structural arrangement which results in an irregular shape of the fuel tank and the provision of structural components extending in the fuel tank, together with requirements on the size of the fuel pump to be capable of drawing a sufficient volume of fuel, there are restrictions on the location of the fuel pump in the fuel tank. For example, internal structural components restrict the location of the fuel pump. It is therefore difficult to draw all of the fuel from the fuel tank. For example, it is not possible to dispose the fuel pump at the lowest point in the fuel tank; that is the lowest point in the fuel tank is defined as the lowest point to which fuel would flow when the aircraft is in its normal flight attitude. As such, there is a quantity of fuel in the aircraft that cannot be retrieved.
The fuel delivery arrangement is not able to draw all of the fuel contained in the fuel tank. This volume of fuel is therefore trapped in the fuel tank, and is not usable. This fuel is known as residual fuel. The residual fuel is excess weight carried by an aircraft which contributes to an increase in aircraft weight, a reduction in the efficiency of the aircraft, and reduces the volume of usable fuel that the aircraft is capable of carrying.